Simultaneous Electrochemical Exfoliation and Covalent Functionalization of MoS 2 Membrane for Ion Sieving.

Transition metal dichalcogenide membranes exhibit good antiswelling properties but poor water desalination property. Here, a one-step covalent functionalization of MoS ₂ nanosheets for membrane fabrication is reported, which is accomplished by simultaneous exfoliating and grafting the lithium-ion-intercalated MoS ₂ in organic iodide water solution. The lithium intercalation amount in MoS ₂ is optimized so that the quality of the produced 2D nanosheets is improved with homogeneous size distribution. The lamellar MoS ₂ membranes are tested in reverse osmosis (RO), and the functionalized MoS ₂ membrane exhibits rejection rates of >90% and >80% for various dyes (Rhodamine B, Crystal Violet, Acid Fuchsin, Methyl Orange, and Evans Blue) and NaCl, respectively. The excellent ion-sieving performance and good water permeability of the functionalized MoS ₂ membranes are attributed to the suitable channel widths that are tuned by iodoacetamide. Furthermore, the stability of the functionalized MoS ₂ membranes in NaCl and dye solutions is also confirmed by RO tests. Molecular dynamics simulation shows that water molecules tend to form a single layer between the amide-functionalized MoS ₂ layers but a double layer between the ethanol-functionalized MoS ₂ (MoS ₂ -ethanol) layers, which indicates that a less packed structure of water between the MoS ₂ -ethanol layers leads to lower hydrodynamic resistance and higher permeation.
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